Solving production down time with parallel low pressure sensors

ABSTRACT

An in-process method and apparatus for monitoring and correcting or replacing a low pressure sensor that gives incorrect low pressure readings because of being contaminated or defective during the formation of integrated circuit structures in a low pressure chemical vapor deposition chamber, where deposition rates are a function of gas flow, temperature, and chamber pressure.

This is a continuation of application Ser. No. 08/657,132, filed Jun. 3,1996, now abandoned.

BACKGROUND OF THE INVENTION

(1) Technical Field

This invention pertains to a thin film deposition process for formingintegrated circuit structures, and more specifically relates to a novelmethod for reducing production down time caused by condensation effectson the pressure sensor that measures Low Pressure in the Chemical VaporDeposition chamber

(2) Description of the Prior Art

The following two documents relate to various methods dealing withsensing of process parameters during deposition of thin film in a lowpressure environment.

U.S. Pat. No. 5,443,997 issued Aug. 22, 1995 to Chiu-Wing Tsui et al,discloses a method of controlling the flow and monitoring the pressureof gases.

U.S. Pat. No. 5,348,614 issued Sep. 20, 1994 to Chris Jerbic discloses aprocess for adjusting the concentration and monitoring the flow ofreactant gases.

During the deposition processing of substrates such as semiconductorwafers to form integrated circuit structures thereon, the condensationin the vacuum chamber eventually builds up and contaminates the pressuresensor (gauge) effecting a zero point shift, hence, indicating amisleading chamber pressure. The zero point is the pressure at which theinstrument displays zero pressure. Because deposition rates are afunction of gas flow, reactor temperature, and total pressure, it isimperative that these parameters be controlled precisely.

An experienced operator is needed to empirically determine when the zeropoint shift is about to occur since no other references are at hand. Iffor example, an operator determines, empirically, that it is time toadjust the pressure sensor since a zero point shift is imminent, thedeposition station is shut down, the pressure sensor is removed andreplaced and a test run is done with the new sensor in place. Between 4to 5 hours are lost each time a defective sensor is replaced. The usefullifetime of a sensor in this environment is only 1 month.

It would, therefore, be desirable to be able to provide a method andapparatus for the formation of integrated circuit structures wherein theeffects of condensation build up on the pressure sensor during oxideetch or any of the chemical vapor deposition processes can be monitoredand compared to a process pressure standard and adjusted accordinglywithout production interference or lost time.

SUMMARY OF THE INVENTION

The present invention provides an improved method for measuring andcorrecting pressure reading errors caused by condensation build-up inthe pressure sensor circuit.

It is a primary object of the present invention to provide apparatus tocompare the deposition pressure against an accessable reference sensorreading and to correct the deposition pressure by adjusting the zeropoint shift and linearity means to match the reference pressure withoutneeding to shut down the system.

It is a another object of the present invention to provide a process forthe removal and replacement of a defective pressure sensor withoutneeding to shut down production for a test run.

These objects are achieved by installing a second in-line valve(manually operated), a second sensor and a second pressure indicatorthat are all mounted in series and then mounted parallel to the firstset of pressure sensing components. When a zero shift or slope changerequires adjustment, the manual in-line valve is opened to conduct thechamber pressure to the second (reference) sensor. Adjustment is made tothe first sensor's adjustment means until its displayed pressurecoincides with the displayed reference pressure. The manual valve isthen turned off thus shielding the reference sensor from the processcontaminants.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of the preferred embodiment of the invention as illustratedin the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in a symbolic schematic drawing the prior artapparatus that is used for measuring pressure in a low pressuredeposition chamber.

FIG. 2 illustrates the present invention improvemnts to a conventionallow pressure deposition chamber.

FIG. 3 is a calibration curve depiction of the "zero point shift".

FIG. 4 is a calibration curve depiction of both "zero point and slopeshift".

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An aspect of the present invention is concerned with improvements to themethods and apparatus used for adjusting and calibrating low pressuresensors in semiconductor processes.

Referring to the drawings and especially FIG. 1 thereof, a conventionallow pressure deposition or chamber 2 is generally indicated to bestdemonstrate the restraints and difficulties when adjusting the readoutfor the zero shifted sensor. Chamber 2 comprises enclosure wall 6, anevacuation port 4 which is connected through in-line valve 5 and pipe 18to an external pumping source (not shown) to maintain the desiredpressure in chamber 2. Pressure is conducted to sensor 10 through port 3which is connected by pipes 16, 17 and on through in-line valve 7.

When a zero point shift is imminent electrical power to chamber 2 isshut off closing in-line valves 5 and 7 (urged to closed positionwithout power). Chamber 2 is exhausted to atmosphere permitting sensor10 to be removed for recalibration and replaced with a new or arecalibrated sensor. Power is restored and a test run is performed toadjust the pressure level of vessel 2. This operation requires 4 to 5hours of lost production time to complete.

In accordance with the invention, the method to adjust for zero pointshift and linearity, or, for the removal and replacement of a defectivepressure sensor without loss of production time includes the steps ofadding bifurcated union 8, manually operated valve 9, reference sensor11 and a digital readout 18 as best illustrated in FIG. 2. If a zeroshift is suspected, opening manual valve 9 permits conduction ofchamber's 2 pressure to be displayed on the reference readout 18 andcompared against the pressure displayed on the process readout 19. Ifthere is no apparent zero shift then manual valve 9 is manually closed,if a shift is detected then manual valve 9 is kept open for theadjustment procedure. Referring to and best explained in FIGS. 2,3 and4, zeroing suggests adjusting the readout 19 for sensor 10. Turningadjustment screw 13, on sensor 10, clockwise lowers a positive shiftwhile turning it counter clockwise raises a negative shift. The zeropoint is the pressure at which the instrument displays zero pressure.For low pressure sensors of the type conventionally used in depositionchambers, zero point is the output voltage at which zero pressure isreferenced. Zero adjustment is an additive/subtractive process whichmoves a sensors's range up or down on the pressure axis. Gradients 30and 34 (FIG. 3) graphically represent a positive and negative zeroshifted pressure whose magnitude is displayed on pressure indicator 19and corrected by either lowering or raising its zeros respectively tocorrespond to its reference pressure as displayed on pressure indicator18 also shown by gradient 32.

FIG. 4 illustrates a sensor's slope change along with a zero pointshift. The zero shift is corrected as previously described. The slopecorrection adjusts the upper range of sensor 10 which may have drifteddue to contamination or aging. After the deposition cycle has beencompleted and chamber 2 is exhausted to 760 torr (atmospheric pressure)the sloped curves 35 and 36, as illustrated in FIG. 4, are corrected byturning slope adjustment screw 14 on in-line valve 10 until its pressurereading displayed on pressure indicator 19 matches the referencepressure displayed on pressure indicator 18.

Condensation will eventually damage the sensor. This becomes evidentwhen shifts and slopes can no longer be adjusted to zero reference. Tothis end, sensor 10 must be replaced. In order to effect a continuousprocess, manual valve 9 is opened while valve 7 is closed, sensor 11will temporarly serve as the in-process monitor until sensor 10 isreplaced. After replacing sensor 10, in-line valve 7 is opened andmanual valve 9 is closed since there is no need to run the lengthy testprocedure for the pressure adjustment in vessel 2 since the new sensor'szero is the same as the reference sensor's zero.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method of adjusting and calibrating acontaminated low pressure sensor without removing it from a depositionchamber to which it is coupled, comprising the steps of:a) Manuallyopening a manual in-line valve to transmit the deposition chamber'sprocess pressure to a reference sensor wherein both manual in-line valveand reference sensor are in series and disposed in a parallel path withthe contaminated low pressure sensor; b) manually adjusting thecontaminated sensor for a zero point shift or for a slope change untilits reading coincides with the reference sensor's reading; and, c)manually closing the manual in-line valve thereby preventing needlessexposure of the reference sensor to process contaminents, whereby sensorcalibration and sensor replacement downtime is greatly reduced.
 2. Themethod of claim 1 wherein said manually adjusting the contaminatedsensor without removing it from the deposition chamber involvesadjusting a zero point shift during a semiconductor process cycle byturning a first adjustment screw located on the output end of thecontaminated sensor until its reading coincides with the referencesensor's reading.
 3. The method of claim 2 wherein turning said firstadjustment screw in one direction lowers said zero point shift andturning it in the opposite direction raises said zero point shift. 4.The method of claim 1 wherein manually adjusting the contaminated sensorfor a slope change, after a chemical vapor deposition cycle is completedand the deposition chamber's process pressure is at atmosphericpressure, by turning a second adjustment screw located adjacent thefirst adjustment screw at the output end of the contaminated sensor. 5.The method of claim 1 wherein turning said second adjustment screw inone direction corrects a negative slope and turning it in the oppositedirection corrects a positive slope.